Cross-Spectrum Microphone Calibration Service - USA

[lovebohn]

Ricci wrote:

Herb,

Do you know what the useable spl limit for the ECM8000 is? Seems to be about 120db or less?

Good question!

[Anechoic]

Ricci wrote:

Herb,

Do you know what the useable spl limit for the ECM8000 is? Seems to be about 120db or less?

I've tested it up to 114 dB with no problems. When I get back from my trip I'll run some tests and see if I can find a definitive limit.

[Ricci]

Anechoic wrote:

I've tested it up to 114 dB with no problems. When I get back from my trip I'll run some tests and see if I can find a definitive limit.

That'd be great. I seemed to have run into some output/ distortion limits with the mic while doing some close mic (2 or 3") low frequency tests. The apparent level that close up to the driver cone was somewhere between 120-125db.

[Anechoic]

Ricci wrote:

That'd be great. I seemed to have run into some output/ distortion limits with the mic while doing some close mic (2 or 3") low frequency tests. The apparent level that close up to the driver cone was somewhere between 120-125db.

I just ran a quick test comparing the distortion of my one of my reference mics (ACO Pacific 7052, rated to 144 dB) to an ECM8000 at 1 kHz.

At 115 dB, my ref mic gets 0.13% distortion, the ECM8000 reads 0.54%

At 120 dB, my ref mic gets 0.22% distortion, the ECM8000 reads 0.81%

At 125 dB, my ref mic gets 0.46% distortion, the ECM8000 reads 1.37%

[Ricci]

Thanks Herb.

Overall that doesn't seem too bad, but it looks like you want to keep things under 120db if you can for the ECM8000. Do you think that there would be a difference if the frequency was lower at like 32hz or 40hz?

[Anechoic]

I'm falling behind trying to cal all those mics I sold last week, but when I get a chance, I'll run the test again at a lower frequency.

[Ricci]

Thanks again for being so forthcoming with data and help with odd requests and questions. I think this distortion info will be very interesting for a lot of people.

I'm going to go ahead and guess that there will be noticeably higher distortion on the LF test. Won't the lower frequencies cause greater deflection of the mics diaghram for a set SPL?

[Anechoic]

Ricci wrote:

I'm going to go ahead and guess that there will be noticeably higher distortion on the LF test.?

Tests at 30 Hz:

At 115 dB, my ref mic gets 1.8% distortion, the ECM8000 reads 3.1%

At 120 dB, my ref mic gets 2.95% distortion, the ECM8000 reads 5.0%

At 125 dB, my ref mic gets 4.2% distortion, the ECM8000 reads 7.4%

FWIW, this is a different ECM8000 than the one used for the 1 kHz test.

[Ricci]

Well...That's eye opening. That could explain some of the things I was seeing. I can only assume that the distortion will get even higher the lower the frequencies get. Looks like you should keep things under 110db when using this mic to remain clean. Not that any one serious about high SPL measurements would be using an ECM8000 in the first place.

Do you think that the ECM will compress the signal somewhat above 120db?

[Anechoic]

Ricci wrote:

Well...That's eye opening. That could explain some of the things I was seeing. I can only assume that the distortion will get even higher the lower the frequencies get. Looks like you should keep things under 110db when using this mic to remain clean.

That sounds like good advice.

Do you think that the ECM will compress the signal somewhat above 120db?

I think that it depends on the mechanism that is causing the distortion, but my guess would be that you would see clipping rather than compression. I'll have to but the mic on an o-scope and check some waveforms at high amplitudes to see what's going on.